Hydraulic control valve

ABSTRACT

There is described an hydraulic control valve comprising a body member pierced by parallel channels and containing three valve chambers. The first and third valve chambers each communicate with both channels. Apertures respectively at one end, intermediate the ends and at the other end of the second valve chamber communicate by way of respective conduit means within the body member each with a respective port in a surface of the body member and respectively with the first and second channels and the first valve chamber. Reversible stop means in the conduit means permit different valve functions to be performed by valve means contained in a plurality of the valve chambers.

United States Patent Inventors Appl. No. Filed Patented Assignee Priority HYDRAULIC CONTROL VALVE 10 Chi end of the second valve chamber communicate by way of 11 Drawing Figs respective conduit means within the body member each with a [1.8.0 respective port in a surface of the body member and respecl /2 tively with the first and second channels and the first valve cl 51/00 chamber. Reversible stop means in the conduit means permit Field of Search 137/269, diff t valve functions to be performed by valve means conl 608 tained in a plurality of the valve chambers.

-4 r-vwfi Primary Examiner-Samuel B. Rothberg Assistant Examiner-William H. Wright Attorney-Lawrence E. Laubscher ABSTRACT: There is described an hydraulic control valve comprising a body member pierced by parallel channels and containing three valve chambers. The first and third valve chambers each communicate with both channels. Apertures respectively at one end, intermediate the ends and at the other PATENTEUNnv 9 Ian SHEET 2 BF 6 FIG. .3.

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Q l H \Q INVENTOR ATTORNEY HYDRAULIC CONTROL VALVE DESCRIPTION OF THE INVENTION This invention relates to a pressure control valve useful in hydraulic control systems.

The valve is particularly though not exclusively suitable for use in control systems using valve mounting blocks of the kind described in a US. Pat. application by Michael A. Jeans and Frank O. Baines filed on May 25, 1970 and entitled MOUNTING BLOCK FOR FLUID CONTROL VALVE.

It is an object of the present invention to provide a pressure control valve which is conveniently adaptable to perform different functions.

It is a more specific object of the invention to provide a valve which, by varying assembly of the same component parts, may function as a pressure relief valve, as an internal pilot sequence valve, as an external pilot sequence valve, or as a constant-pressure valve.

It is a further object of the invention to provide a pressure control valve having advantages when used in hydraulic control systems comprising a nexus of control valves.

An embodiment of hydraulic control valve according to the invention comprises a body member having two opposite parallel faces. First and second parallel channels within the body member extend between the two faces. The body member contains first, second and third valve chambers of which the first and third each communicate with both of said channels. A first aperture at one end of the second valve chamber communicates by way of first conduit means within the body member with a first port in a surface of the body member and with the first channel. A second aperture intermediate the ends of the second valve chamber communicates by way of second conduit means within the body member with a second port in a surface of the body and with the second channel. A third aperture at the other end of said second valve chamber communicates by body member of third conduit means within the body member with a third port in a surface of the body member and with said first valve chamber. The body member and with said first valve chamber. Valve means are provided within each of a plurality of said valve chambers for controlling the flow of fluid between said channels.

Features and advantages of a valve incorporating the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, of which:

FIG. 1 is a plan of a pressure relief valve;

FIG. 2 is a front elevation of the valve shown in plan in FIG.

FIGS. 3 and 4 are sectional elevations of the valve taken along corresponding numbered lines 3--3 and 4-4 in FIGS. 1 and 2, and

FIGS. 5-9 are schematic diagrams illustrating the operation of the valve in different modes; and

FIGS. A and 10B are schematic diagrams illustrating an advantageous modification of the valve.

The valve shown in the drawings comprises a metal block 10 pierced by parallel channels 11 and 12 and optionally by an additional channel 13. When the valve is to be used in conjunction with a mounting block of the kind described in the above-mentioned application by JEANS and BAINES channels 11, 12 and associated fastening holes 14 which also pierce block 10 parallel to channels 11, 12, are disposed in the pattern of symmetry defined by the corresponding ports and holes of the mounting block.

As shown in FIG. 3, a passage 15 formed in the valve body leads from channel 11 by way of two right-angle bends of which a first is formed by the intersection of drilled holes entering the block through perpendicular faces. The first of these holes passes vertically downwards through the center of channel 11, as shown in FIGS. 3 and 4, and that part of the hole between channel 11 and the block surface is closed by screw plug 15a. The second bend is formed within a sealing sleeve 16 which is sealed against hydraulic pressure by an O- ring 17. The sleeve is retained in position by a screw-threaded plug 18 which itself may be sealed to the valve body 10 by a washer 19. Sleeve 16 has a central port 16a communicating with channel 15 and itself communicating by way of radial ports 16b interconnected by a circumferential channel 16c, with a further passage 20 formed in the valve body. Passage20 leads by way of a first aperture into one end of a first valve chamber 21 into which is screwed a primary valve sleeve 22 which is sealed to the valve body by O-rings 23, 24 and by a washer 25.

Sleeve 22 is provided with two axially spaced rings of ports 33, 34 at different axial positions. Within the bore 22b of sleeve 22 slides a valve spool 26, which is resiliently biased. Specifically, valve spool 26 is urged inwardly of the sleeve by coaxially disposed helical compression springs 27a, 27b which bear against the valve spool and abut against a sealing plug 28. Plug 28 abuts against a screw-threaded spring-adjuster member 29 which screws into valve sleeve 22 and is locked by a nut 30, and is sealed to the bore in sleeve 22 by O-rings 28a. Valve spool 26 is provided with a guide spindle or stem portion 26a which extends through a bore in sealing plug 28 into a central bore 31 in adjuster member 29 and is sealed to a sealing plug 28 by an O-ring 28b. Inward movement of valve spool 26 is limited by the engagement of an outwardly extending flange 26b formed on spool 26 with engagement of an outwardly extending flange 26b formed on spool 26 with a shoulder 22a formed in the bore of valve sleeve 22 to a position in which a barrel portion of the valve spool closes ports 34. Valve spool 26 is pierced by a central bore 26c which enters a cross bore 26d formed in stem portion 26a seats to connect spring chamber 22 with valve chamber 24. By this means the hydraulic pressure in valve chamber 21 and sleeve bore 22b is equalized, so that the effective pressure upon valve spool 26 is that due to the hydraulic pressure in the valve chamber acting upon the difference between the areas exposed to the pressure in the valve chamber and in the sleeve bore 22b. This difference is determined by the relative diameters of the valve spool and of the valve stem.

When the pressure applied from channel 11 to the end of the valve spool by way of passages 15 and 20 exceeds that necessary to overcome the resilient bias provided by the pressure of springs 27a, 27b, valve spool 26 will be moved to permit port rings 33, 34 to communicate with one another by way of a central annular groove 26e embracing the spool. Thus when this action occurs, the outer ring 34 of valve ports is put in communication with channel 12 by way of passages 35. 36 formed in the valve body and communicating with one another by way of passages formed within a sealing sleeve 37 sealed by an O-ring 38 and held in the valve body by a spacer 39 supported by a screw-threaded plug 40-itself sealed by a washer 41. Passage 35 enters valve chamber 21 by way of a second aperture formed medially therein.

Port ring 34 in valve sleeve 22 communicates by way of a passage 42 formed in the valve body with a second valve chamber 43, shown in FIG. 4. Passage 42 enters valve chamber 21 by way of a third aperture formed at the other end thereof. Into second valve chamber 43 is sealed by means of a sealing washer 44 a secondary valve plug member 45. Third valve chamber 43 is connected with the second aperture of second valve chamber 21 by way of a passage 42 within the valve body. Passage 42 also leads to a third port in a face of the valve body, which may be closed by a screwed plug 69 (see FIG. 2). The passage 42 communicates with a circumferential channel 46 formed in the valve plug 45, which channel communicates by way of a diametral bore 47 and an axial passage 47a with the interior of a valve sleeve 48 positioned inwardly of valve plug 45 in second valve chamber 43. Sleeve 48, has at its inner end a valve seat 49 against which a secondary valve 50 is urged by a helical spring 51. Spring 51 abuts at each end against a respective one of centrally apertured spring rest 52, 53. The end of secondary valve spool 50 is pierced by a vent 54 permitting a slow flow of fluid from channel 11 to the interior of the valve spool. The innermost end of valve sleeve 48 is sealed to the wall of valve chamber 43 by sealing rings 55. A third valve chamber 56 communicates directly both with channel 11 and with channel 12. For many purposes this third valve chamber is not employed and it is then sealed by a laterally apertured sealing plug which is used to hold sealing rings against the walls of the chamber intermediate channels 1 1 and 12. For other applications, as shown in the drawings, a nonreturn valve may be fitted in third valve chamber 56 to permit fluid to flow freely from channel 12 to channel 11 when the latter channel contains fluid at a lower pressure.

The nonreturn valve may comprise a screw-threaded valve sleeve 57 which is sealed to valve body by a washer 58 and fills a bore communicating with channels 11 and 12. Sleeve 57 is provided at 59 with a valve seat against which bears a valve 60. Valve 60 is resiliently urged against seat 59 by a helical compression spring 61 of which the ends bear against the head of valve 60 and against a plug 62 which fits tightly in the bore of sleeve 57 and is retained by a spring clip 63 fitted in a groove in the sleeve bore or by other suitable means. Sleeve 57 is laterally apertured at 64 to provide communication between the portions of channel 11 which lie on either side of the sleeve. Valve 60 is laterally apertured at 65 so that when the pressure in channel 12 exceeds that in channel 11, and the valve therefore moves inwardly of the sleeve, fluid may flow from channel 12 to channel 11 by way of apertures 65.

Channel 13 formed in valve body 10 may be employed for the passage of electrical control leads for other valves associated with the relief valve.

The operation of the valve as a pressure relief valve will now be described with special reference to FIG. 5. In the normal or unactuated condition, the fluid pressure above and below secondary valve spool 50 is equalized by way of aperture 54 in the head of the valve spool. Thus the secondary valve is closed and fluid cannot pass from channel 11 to channel 12. When the fluid pressure in channel 11, communicated by way of passages 15, to the primary valve chamber 21, reaches the set valve and overcomes the pressure exerted on primary valve spool 26 by spring 27, the primary valve spool 26 is depressed, thus putting secondary valve chamber 43 in communication with channel 12 and allowing flow through the equalizing base 26c. Secondary valve spool 50 is then depressed against the pressure of secondary valve spring 51 by the pressure difference appearing across the valve spool 26, thus opening the secondary valve by an amount such that fluid flows from channel 11 to channel 12, at a rate such as to eliminate any excess of pressure over the set value. This type of valve is used on almost every hydraulic circuit to protect the circuit from overloading.

FIG. 6 shows the operation of the valve when assembled to form a pilot-operated check valve or relay valve. This mode is achieved by reversing a sealing sleeve, which is retained by a screw-threaded plug 69 (FIG. 2), in the passage 42 by which secondary valve chamber 43 was previously in communication with ports 34 of the primary valve and making a pipe connection 70 in place of the plug. This type of valve would be used on, say, a press control circuit, where the circuit is required to be inoperative until certain guards are in position. Each guard operates a small valve through which the external signal flow can return to tank when the guard is not in position. When all the guards are in position, there is no flow down the external signal line and the poppet remains on its seat. Pressure can then be built up in the supply line and the hydraulic circuit becomes operative. As soon as any guard is lifted, the flow down the external signal line allows the poppet to rise and dump the whole supply flow into the return line, thereby making the circuit inoperative.

FIG. 7 illustrates the operation of the valve as a sequence valve with internal pilot operation. This mode is achieved by inverting sealing sleeve 37 to close passage 36 and replacing spacer 39 and plug 40 by a pipe connection 70 providing an external drain. This type of valve is used to permit the application of pressure to a device, connected to channel 12, only when the pressure within channel 11 attains the value set by the spring pressure of the primary valve 26. Such a valve might be used where the hydraulic circuit contains more than one hydraulic jack or motor, and it is designed to protect one of these jacks or motors from load fluctuations on the remainder. Therefore, if the load fluctuations on the remainder are such that the system pressure drops below the setting of the sequence valve, the valve disconnects those items from the hydraulic circuit. When the inlet pressure is above the set pressure, the spool first stage allows flow through the poppet equalizing passage into an external drain. The poppet valve 50 lifts off its seat and permits flow into the sequence line and hence to the jacks or motors that are liable to have load fluctuations. As soon as the fluctuations reduce the system pressure so as to impair the operation of the important jack or motor, there is no longer sufiicient pressure to hold the spool 26 off its seat and so flow through the poppet equalizing passage is cut off. The poppet 50 moves on to its seat and cuts off all flow to the sequence line.

FIG. 8 shows how the valve may be arranged to operate as a sequence valve with external pilot operation. This mode is achieved by inverting sealing sleeves l6 and 37 in passages 15 and 36 and making appropriate external connections 71 and 72 in place of plugs 18 and 40. Pipe 71 now receives an external pilot signal; when the pressure applied by way of pipe 71 to the first aperture of second valve chamber 21 exceeds the value corresponding to the bias of spring 27, valve spool 26 will be moved to an actuated condition in which the third valve chamber is connected with drain pipe 72. This action reduces the pressure in valve chamber 43 and thus permits valve 50 to open and allow liquid to pass from channel 11 to channel 12. When valve 26 is allowed to close, by removal of the pilot signal, the pressure in valve chamber 43 is rapidly raised by leakage through vent 54, whereupon springs 51 returns valve poppet 50 into valve seat 49 to close the valve. This type of sequence valve may be used, for instance, on a clamping circuit. The pressure in the clamping cylinder must reach a certain level, i.e., the object must be clamped before a press or drill can be allowed to descend on the object and perform the next operation. When the object has been clamped and the pressure in the clamping cylinder reached the necessary level, flow again comes through the poppet equalizing passage and the poppet rises off its seat to allow flow into the sequence line to operate the press or drilling cylinder. It should be noted that in both types of sequence valve there is very often a check or nonreturn valve to allow completely free flow from the sequence line back into the inlet line. This has been included in the diagrams shown.

FIG. 9 shows how the use ofa modified spool for the primary valve enables the valve to be used to provide a constant, reduced pressure in channel 12. The valve is modified from the configuration of FIG. 5 by inverting sealing sleeve 16, removing sleeve 37 and providing an external conduit means, here shown as a pipe connection 75 between the ports 20a, 35a at which channels 35 and 20 emerge from the body 10. The operation of the valve in this mode is that whenever the pressure in channel 12 exceeds that determined by the pressure of spring 27 on primary valve spool 26, the valve spool will be moved inwardly of the valve chamber to close ports 33. Secondary valve chamber 43 is thus isolated from channel 12 and the pressure on either side of secondary valve spool 50 will be equalized. The valve will therefore close. A fall ofpressure in channel 12 will permit primary valve spool 26 to uncover ports 33, thus reducing the pressure in secondary valve chamber 43 and allowing valve 50 to open.

FIGS. 10A and 108 show diagrammatically a possible modification of the primary valve whereby the mode of operation of FIG. 9 may be obtained by the mere inversion of the valve spool, rather than its modification. In this embodiment spool extension 26a is dispensed with and the spool portion 26d which opens and closes the valve ports is so formed that, when this portion is placed outermost of valve chamber 24, as in FIG. 10A, movement of valve spool 26 against the pressure of spring 27 will uncover ports 34. When spool portion 26d is placed innermost, as in FIG. B, then movement of spool 26 against spring 27 will close ports 35. The inversion of the valve spool enables the valve to be used in the modes described in relation to FIGS. 7 and 8 as a sequence valve to cut off flow to the sequence line when a set pressure is reached.

The through channels make the valve not only a very useful addition to the kind of manifold described in copending application by JEANS and BAlNES above referred to, but also makes it compatible with any specially designed manifold, such as might be used for a metal press or plastic injection molding machine. The valve need only be screwed on to the manifold block with the appropriate two passages connected into the block. This saves the additional passages that will be required in the block when a conventional valve is fitted. In the case of the conventional valve which is manifold mounted, no outlet connections can be made to the valve, and they all have to be made through the manifold block. The result is that the flow has to come into the manifold block, through the valve and then back into the manifold block again. This means that a very considerable saving in terms of cost of drilling passages is made when a valve with through passages is mounted on a manifold block.

As a result of using through passages for the main circuit the flow rating of the valve, if this is nominally a l zinch valve, at least equal the rating of many commercially available 92inch valves. This is because the two main passages are very large and the secondary poppet is so designed as to connect them with a minimum of restrictions.

The almost complete interchangeability of the valve parts for its different methods of operation offers very considerable savings in production costs, as only one basic type of valve has to be produced to meet several different applications.

Since the valve is produced as a body with several inserts, the main inserts being the first stage spool assembly, the second stage poppet assembly, and, if required, a check valve assembly, any maintenance which may become necessary consists of no more than removing the defective assembly and inserting a replacement.

In the specific embodiments described the pilot valve spool 26 is provided with a equalizing bore 261: so that the effective pressure on the spool is the applied hydraulic pressure multiplied by the difference in areas of the valve end faces, one of these end faces being reduced in area by the presence of guide spindle 26a. This arrangement enables lighter springs 27 to be used, but requires the sealing of guide spindle 26a against the hydraulic pressure, with some resulting friction. This disadvantage may be overcome by reducing the diameter of the valve spool so that the absolute pressure may be balanced by conveniently available springs. As a guide spindle is then no longer required the reversible spool construction of FIGS. 10A and 10B is thus very conveniently adopted.

We claim:

1. An hydraulic control valve comprising in operative combination:

a body member having two opposite parallel faces;

first and second parallel channels within said body member extending between said faces;

first, second and third valve chambers within said body member, said first and third valve chambers each communicating with both of said first and second channels;

a first aperture at one end of said second valve chamber;

a first port in a surface of said body member;

first conduit means within said body member connecting said first aperture with said first port and with said first channel;

a second aperture intermediate the ends of said second valve chamber;

a second port formed in a surface of said body member;

second conduit means within said body member connecting said second aperture with said second channel and with said second port;

a third aperture at the other end of said second valve chamber;

a third port in a surface of said body member;

third conduit means within said body member connecting said third aperture with said first valve chamber and with said third port;

and valve means in each of a plurality of said valve chambers for controlling the flow of fluid between said channels.

2. The control valve claimed in claim 1 wherein said third valve chamber contains resiliently biased nonreturn valve means permitting fluid flow therethrough only from said second channel to said first channel.

3. The control valve claimed in claim 1 wherein said first valve chamber contains sequence valve means resiliently biased to a condition in which fluid flow therethrough between said channels is prevented, said sequence valve means being operable by fluid pressure within said first channel in response to release of fluid pressure within said second conduit means to permit fluid flow from said first to said second channel;

and wherein said second valve chamber contains spool valve means resiliently biased to a condition in which communication between said chamber apertures is prevented, said spool valve means being operable against said bias by pressure within said first conduit means to an actuated condition in which fluid flow is permitted between said second and third conduit means.

4 The control valve claimed in claim 3 wherein each said conduit means contains means preventing fluid flow through the respective one of said ports, whereby said spool valve means is actuated by increase of pressure in said first channel above a predetermined value set by the resilient bias therein to produce actuation of said sequence valve means to permit fluid flow from said first channel to said second channel thereby to prevent further increase of pressure in said first channel.

5. The control valve claimed in claim 3 wherein each of said first and second conduit means contains stop means preventing fluid flow through the respective one of said ports and wherein said third conduit means contains means permitting fluid flow only between said second channel and said third port, whereby said spool valve means is operable by fluid pressure within said first channel to permit discharge of fluid from said second valve chamber to said second channel and thus to produce actuation of said sequence valve means.

6. The control valve claimed in claim 3 wherein said third conduit means contains stop means preventing fluid flow through said third port, said first conduit means contains stop means preventing fluid flow between said first channel and said first aperture and said second conduit means contains stop means preventing fluid flow between said second aperture and said second channel, whereby said spool valve means is operable by fluid pressure applied to said first port to permit discharge of fluid from said second valve chamber through said second port thereby to permit actuation of said sequence valve means.

7. The control valve claimed in claim 3 wherein said first conduit means contains stop means permitting fluid flow only between said first aperture and said first port, said second conduit means permits fluid flow between said second channel, said second aperture and said second port, further conduit means couples said first and second ports for fluid flow therebetween and said third conduit means contains stop means permitting fluid flow only between said second valve chamber and said third aperture, whereby said spool valve means is actuated in response to the fluid pressure in said second channel falling below a predetermined pressure to permit fluid flow from said first to said second channel.

8. The control valve claimed in claim 1 wherein said first valve chamber contains sequence valve means operable in response to release of fluid pressure within said chamber to permit fluid flow from said first to said second channel and wherein said third conduit means contains stop means permitting fluid flow only between said second valve chamber and said third port whereby the passage of fluid from said first channel to said second channel through said sequence valve being operable against a resilient bias between a first position in which said barrel portion closes a said set of ports in a second position in which said portion of reduced diameter permits fluid flow between said sets of ports.

10. The control valve claimed in claim 9 wherein said piston means includes a guide spindle, said sleeve means having sealing means through which said spindle extends into a space sealed by said sealing means against fluid pressure. 

1. An hydraulic control valve comprising in operative combination: a body member having two opposite parallel faces; first and second parallel channels within said body member extending between said faces; first, second and third valve chambers within said body member, said first and third valve chambers each communicating with both of said first and second channels; a first aperture at one end of said second valve chamber; a first port in a surface of said body member; first conduit means within said body member connecting said first aperture with said first port and with said first channel; a second aperture intermediate the ends of said second valve chamber; a second port formed in a surface of said body member; second conduit means within said body member connecting said second aperture with said second channel and with said second port; a third aperture at the other end of said second valve chamber; a third port in a surface of said body member; third conduit means within said body member connecting said third aperture with said first valve chamber and with said third port; and valve means in each of a plurality of said valve chambers for controlling the flow of fluid between said channels.
 2. The control valve claimed in claim 1 wherein said third valve chamber contains resiliently biased nonreturn valve means permitting fluid flow therethrough only from said second channel to said first channel.
 3. The control valve claimed in claim 1 wherein said first valve chamber contains sequence valve means resiliently biased to a condition in which fluid flow therethrough between said channels is prevented, said sequence valve means being operable by fluid pressure within said first channel in response to release of fluid pressure within said second conduit means to permit fluid flow from said first to said second channel; and wherein said second valve chamber contains spool valve means resiliently biased to a condition in which communication between said chamber apertures is prevented, said spool valve means being operable against said bias by pressure within said first conduit means to an actuated condition in which fluid flow is permitted between said second and third conduit means. 4 The control valve claimed in claim 3 wherein each said conduit means contains means preventing fluid flow through the respective one of said ports, whereby said spool valve means is actuated by increase of pressure in said first channel above a predetermined value set by the resilient bias therein to produce actuation of said sequence valve means to permit fluid flow from said first channel to said second channel thereby to prevent further increase of pressure in said first channel.
 5. The control valve claimed in claim 3 wherein each of said first and second conduit means contains stop means preventing fluid flow through the respective one of said ports and wherein said third conduit means contains means permitting fluid flow only between said second channel and said third port, whereby said spool valve means is operable by fluid pressure within said first channel to permit discharge of fluid from said second valve chamber to said second channel and thus to produce actuation of said sequence valve means.
 6. The control valve claimed in claim 3 wherein said third conduit means contains stop means preventing fluid flow through said third port, said first conduit means contains stop means preventing fluid flow between said first channel and said first aperture and said second conduit means contains stop means preventing fluid flow between said second aperture and said second channel, whereby said spool valve means is operable by fluid pressure applied to said first port to permit discharge of fluid from said second valve chamber through said second port thereby to permit actuation of said sequence valve means.
 7. The control valve claimed in claim 3 wherein said first conduit means contains stop means permitting fluid flow only between said first aperture and said first port, said second conduit means permits fluid flow between said second channel, said second aperture and said second port, further conduit means couples said first and second ports for fluid flow therebetween and said third conduit means contains stop means permitting fluid flow only between said second valve chamber and said third aperture, whereby said spool valve means is actuated in response to the fluid pressure in said second channel falling below a predetermined pressure to permit fluid flow from said first to said second channel.
 8. The control valve claimed in claim 1 wherein said first valve chamber contains sequence valve means operable in response to release of fluid pressure within said chamber to permit fluid flow from said first to said second channel and wherein said third conduit means contains stop means permitting fluid flow only between said second valve chamber and said third port whereby the passage of fluid from said first channel to said second channel through said sequence valve means takes place only in response to release of pressure from said third port and wherein said third valve chamber contains resiliently biased valve means permitting fluid flow only from said second channel to said first channel.
 9. The control valve claimed in claim 3 wherein said spool valve means includes sleeve means having two axially spaced first and second sets of ports communicating respectively with said second and third apertures, piston means having a barrel portion and a portion of reduced diameter, said piston means being operable against a resilient bias between a first position in which said barrel portion closes a said set of ports in a second position in which said portion of reduced diameter permits fluid flow between said sets of ports.
 10. The control valve claimed in claim 9 wherein said piston means includes a guide spindle, said sleeve means having sealing means through which said spindle extends into a space sealed by said sealing means against fluid pressure. 